C# by Examples

Learn how async and await enable asynchronous programming in C#, letting methods suspend execution without blocking the calling thread.

Learn when to use async/await for I/O-bound work versus Task.Run for CPU-bound code that needs to run on a background thread in C#.

Implement the Boyer-Moore string search algorithm in C# for fast pattern matching. Learn how Boyer-Moore works, when to use it over built-in methods, and see complete working examples with performance benchmarks.

Learn how to cast and convert types in C#. Covers explicit cast, implicit conversion, the as and is operators, Convert class, safe casting patterns, and when each approach is appropriate.

Use string.IsNullOrEmpty() to check for null or empty strings in C#. Use string.IsNullOrWhiteSpace() to also catch whitespace-only strings.

Integer overflow in C# silently wraps by default. Learn how checked and unchecked contexts work, when to use them, and how to handle arithmetic overflow safely.

Which C# collection should you use? Compare List, Array, Dictionary, HashSet, Queue, Stack, and LinkedList with Big-O complexity, use cases, and code examples.

const fields are compile-time constants set at declaration. readonly fields are runtime constants that can be assigned in the constructor in C#.

Cast an int to an enum type in C# for a direct conversion. Learn how to safely convert integers to enum values using Enum.IsDefined and Enum.TryParse.

Learn how to convert a string to int in C# with int.Parse, int.TryParse, and Convert.ToInt32. Handle null, empty, invalid, whitespace, and overflow input safely.

Learn C# DateTime.ToString formats for yyyy-MM-dd, yyyyMMdd, HH:mm:ss, ISO 8601, filenames, logs, and common mistakes such as mm vs MM and hh vs HH.

Copy-paste C# DateTime.ToString format examples for yyyy-MM-dd, ISO 8601, logs, filenames, UTC, and localized output.

Learn delegates, lambda expressions, Func<T>, Action<T>, and Predicate<T> in C# with practical examples. Understand how lambdas replace verbose delegate syntax and enable LINQ.

Learn how to add, update, find, and iterate a C# Dictionary. Compare Add, indexer assignment, TryAdd, TryGetValue, and ContainsKey with practical examples.

Dictionary<TKey, TValue> is a generic, type-safe modern collection. Hashtable is a legacy non-generic alternative that stores objects and requires casting.

Learn C# enums with Enum.GetValues, declaration, iteration, Flags, conversion to string, parsing, and practical examples of named integer constants.

Learn how C# events work: declaring events with EventHandler, raising events, subscribing and unsubscribing, creating custom EventArgs, and safe event invocation patterns.

Go beyond basic try/catch in C#: throw vs rethrow, creating custom exception classes, exception filters with when, and best practices for exception handling in production code.

foreach is more readable for simple collection traversal. for loops provide index access, reverse iteration, and custom step sizes for more control in C#.

Generate random numbers in C# using the Random class. In .NET 6+, use Random.Shared for a static, thread-safe shared instance with better performance.

C# generics let you write type-safe, reusable code without casting or boxing. Learn how to create generic classes, generic methods, and apply constraints with the where keyword.

Understand when to use Guid.Empty, default(Guid), and new Guid() in C# and how they compare in guard clauses and nullable code.

Learn how to generate, parse, format, and compare GUIDs in C#. Covers Guid.NewGuid(), Guid.Parse(), TryParse, ToString formats, Guid.Empty, and performance tips.

Learn how to parse GUIDs with Guid.Parse and Guid.TryParse, format them with N, D, B, P, and X, and normalize values for storage or display.

HashSet<T> is optimized for fast lookups and uniqueness. List<T> is ordered, allows duplicates, and provides index access. Learn which to use in C#.

Understand when IEnumerable<T> should be used for in-memory queries and when IQueryable<T> is better for database-backed LINQ.

Interfaces define a pure contract with no implementation. Abstract classes share a base with common code. Learn when to use each design pattern in C#.

Learn what a C# interface is, how to define and implement one, implement multiple interfaces, use explicit members, and choose an interface or abstract class.

Iterate a Dictionary in C# using a foreach loop to access each KeyValuePair, or loop over just the Keys or Values collection properties separately.

Learn how to use string.Join in C# to combine arrays, lists, and IEnumerable values with a separator, including commas, spaces, and custom delimiters.

Use LINQ aggregate methods in C# to compute sums, counts, averages, min/max, and custom reductions. Covers Sum(), Count(), Average(), Min(), Max(), and the general-purpose Aggregate() method.

Use LINQ methods like First, FirstOrDefault, Single, and Any to find elements in C# collections. Learn when to use each to avoid InvalidOperationException.

Use LINQ GroupBy() in C# to group elements by a key selector. Returns groups each containing the key and matching elements from the source collection.

Use LINQ Join() in C# to combine two sequences on a matching key, equivalent to SQL inner join. Only elements with matching keys appear in the result.

Sort with LINQ OrderBy() in C# to get a new sorted sequence without modifying the original. Use ThenBy() for secondary sort keys.

Use LINQ Select() in C# to project each element into a new form. Transforms a collection with a lambda and returns a new IEnumerable with the results.

Filter a collection in C# with LINQ Where() by passing a predicate function. Uses deferred execution and returns only elements satisfying the condition.

Check if a List is empty in C# using the Count property or LINQ Any() method. Prefer Any() for IEnumerable types to avoid full enumeration overhead.

Arrays have a fixed size and are memory-efficient in C#. Lists are dynamic, resize automatically, and provide methods like Add(), Remove(), and Contains().

Merge two C# lists using LINQ Concat() for a clean readable result, or AddRange() to append elements directly into an existing list in place.

The ?? operator returns the left operand if not null, otherwise the right. Use ??= to assign a default value only when the variable is null in C#.

Nullable reference types in C# 8.0+ make nullability explicit to prevent NullReferenceException. Enable with the Nullable enable setting in your project.

C# nullable value types (int?, bool?, DateTime?) let value types represent the absence of a value. Learn Nullable<T>, HasValue, Value, GetValueOrDefault, and common null-handling patterns.

Use int.Parse() when the string is guaranteed valid. Use int.TryParse() to safely handle potentially invalid input without throwing an exception in C#.

Learn C# pattern matching with is expressions, switch expressions, type patterns, property patterns, relational patterns, and list patterns.

Learn how C# properties work: auto properties, get/set accessors, init-only properties, computed properties, and the difference between properties and fields.

Generate random integers in C# with Random.Shared.Next, Random.Next, and NextInt64. Learn ranges, repeatability, and when to use RandomNumberGenerator.

Read a text file in C# with File.ReadAllLines() for simplicity, or File.ReadLines() for memory-efficient lazy reading of large files line by line.

Learn the difference between a C# record and class, including value equality, immutability, constructors, with expressions, inheritance, and record struct examples.

ref parameters must be initialized before the call. out parameters must be assigned inside the method. Learn when to use each type of parameter in C#.

Test and use C# regular expressions with examples for IsMatch, Match, Groups, named captures, Replace, validation, and common regex patterns.

Remove duplicates from a C# list using LINQ Distinct() or by converting to HashSet<T>, which automatically stores only unique element values.

Sort a list of objects by property in C# using LINQ OrderBy(), List.Sort() with a lambda, or IComparer. Covers ascending, descending, and multi-key sorting.

Sort a C# list with Sort() for in-place modification, or LINQ OrderBy() for a new sorted sequence that leaves the original list unchanged.

Span<T> and Memory<T> let you slice arrays, strings, and stack buffers without allocating new objects. Learn how to use them to cut allocations, speed up parsing, and write modern high-performance C#.

Learn how to use Stack<T> and Queue<T> in C#. Covers push/pop/peek for stacks, enqueue/dequeue/peek for queues, performance characteristics, and real-world use cases for each.

Compare string[] and List<string> in C# for fixed-size versus dynamic collections, performance, Add and Remove operations, and conversion examples.

Compare strings in C# correctly using ==, .Equals(), or string.Compare(). Understand StringComparison, OrdinalIgnoreCase, CurrentCulture, and when to use each approach.

Learn C# string.Format with format specifiers for numbers, dates, currency, percentages, alignment, and zero-padding, plus examples compared with interpolation.

Use the $ prefix in C# for string interpolation to embed expressions in string literals. It is more readable than string.Format and supports format specifiers.

Learn the most commonly used C# string methods, including Contains, StartsWith, Split, Replace, Trim, Substring, IndexOf, Join, and padding examples.

In C#, string (lowercase) is an alias for System.String. Both compile to the same IL code. Using the lowercase string keyword is the C# convention.

Use StringBuilder in C# for efficient string building in loops. Unlike immutable strings, it reuses the same buffer to avoid repeated memory allocations.

Use a struct for small simple value types like Point or Color. Use a class for complex types with behavior. Structs are stack-allocated value types in C#.

Switch expressions in C# 8.0+ provide concise pattern matching that returns a value directly. They replace verbose switch statements and eliminate break.

Learn how to run multiple async tasks concurrently with Task.WhenAll and Task.WhenAny, and when to use Task.Run to offload CPU-bound work in C#.

Handle exceptions in C# using try-catch-finally. Code in try runs first, catch handles exceptions, and finally always executes for resource cleanup.

Tuple is a reference type from older C# with Item1, Item2 properties. ValueTuple is a C# 7+ value type struct with named members and better performance.

var lets the C# compiler infer the type from the initialization expression. Use explicit types when the type is not obvious from context or for clarity.

A BOM (Byte Order Mark) is a Unicode character indicating a file's encoding and byte order. Learn how to detect and handle BOM characters in C# file I/O.

Write raw text containing < > & " ' to a file in C# and learn when escaping is needed.

Write to a text file in C# using File.WriteAllText, File.WriteAllLines, File.AppendAllText, StreamWriter, and async variants. Includes examples for writing special characters and appending files.